Method of slip casting powdery material, using a water resistant mold with self-water absorbent ability

ABSTRACT

A method of slip casting using a casting mold provided with a water-absorbent layer that has a self-water-absorbent ability, substantially has a water resistance, and is controlled in the saturated water content thereof, the slip casting being conducted by employing mainly a capillary sucking force as the driving force of the water-absorbent layer of cast formation. An open-cell porous body usable as the water-absorbent layer is produced by agitating a mixture comprising a compound having at least one epoxy ring in its molecule, a curing agent which cures the epoxy compound by reaction, a filler developing for a self-water-absorbent ability and a mold release property, and water to prepare an O/W emulsion slurry and curing the slurry, as such in a hydrous state.

FIELD OF THE INVENTION

The present invention relates to a method of slip casting a powderymaterial such as an inorganic, organic, or metallic powdery material, amold for use in a slip casting method, and a method of manufacturing anopen porous body for use in a mold.

DESCRIPTION OF THE RELEVANT ART

Heretofore, molds for slip casting powdery materials have primarily beenin the form of gypsum molds for various reasons. The gypsum molds areinexpensive, can easily be formed to shape, and, most importantly, havethe following two superior properties for use as molds: (1) The gypsummolds have a self water absorption capability (Since some slurries usedin the slip casting process employ an organic solvent rather than water,the term "water" used in the present invention should be interpreted ascovering an organic solvent. Therefore, the water absorption capabilityis meant to include an ability to absorb an organic solvent.) (2) Thegypsum molds allow molded products to be removed with good moldreleasability.

A depositing step in a slip casting process causes water in a slurry tobe absorbed by a porous mold. The water is absorbed by the porous moldunder a differential pressure between a mold surface and a depositionsurface (a boundary surface between a region where the slurry isdeposited and a region where the slurry is not deposited). Thedifferential pressure maybe developed by roughly two mechanisms, i.e.,capillary attractive forces produced by the mold and an externalpressure applied to the mold or the slurry, e.g., the gravity headpressure of the slurry, the forces applied to directly press the slurry,or the suction forces applied to evacuate the mold. The self waterabsorption capability, which is the first advantage of the gypsum molds,is produced by the capillary attractive forces, and allows a slurry tobe deposited without applying an external pressure.

A mold releasing step of removing a molded product from a mold isimportant in the slip casting process. If the molded product is notsmoothly released from the mold, the molded product will be deformed asit is soft. The reason why a gypsum mold provides good moldreleasability is that since gypsum is poor in water resistance, thesurface of the gypsum mold is dissolved into water little by little.Stated otherwise, the good mold releasability provided by the gypsummold is achieved because the molding surface of the gypsum mold ispeeled off together with the molded product.

As described above, the gypsum molds have two advantages, i.e., goodmold releasability and self water absorption capability. Theseadvantages, however, are associated with disadvantages. Because the selfwater absorption capability is achieved by the capillary attractiveforces, the rate at which the slurry is deposited cannot besubstantially increased, posing a limitation on efforts to increase theproductivity. Inasmuch as the good mold releasability is provided bydissolving the molding surface of the mold, the molding surface will begreatly worn when the mold is used in many slip casting processes. Thenumber of products that can be molded by one mold, i.e., the servicelife of one mold, is only in the range from 80 to 150.

In order to eliminate the above shortcomings of the gypsum molds, therehas been used a mold of water-resistant resin. A slurry is deposited inthe mold of water-resistant resin by directly applying a pressure to theslurry. Therefore, when the pressure applied to the slurry is increased,the rate at which the slurry is deposited is also increased. The mold ofwater-resistant resin provides mold releasability which is much lowerthan the gypsum molds. Therefore, it has been customary to deliver airunder pressure to the mold of water-resistant resin, i.e., to apply aback pressure to the mold, for supplying water accumulated in the moldand the air to a boundary surface between the mold and the moldedproduct thereby to release the molded product from the mold.Specifically, Japanese patent publication No. 2-15364 discloses an airgroove defined in a mold, and Japanese patent publication No. 2-15365shows a coarse porous layer disposed on the reverse side of a moldhaving a molding surface. The water and the air are supplied to theboundary surface between the mold and the molded product through the airgroove or the coarse porous layer. Air grooves defined in molds are alsoproposed in Japanese patent publications Nos. 1-49803 and 2-17328.

Porous materials of resin molds for pressure casting include epoxy,acrylic, and unsaturated polyester materials. Among these materials, theepoxy materials are widely used for the reasons of small shrinkage andheat generation upon curing. There have been proposed open porous bodiesas disclosed in Japanese patent publications Nos. 53-2464, 62-26657,5-8936, 5-39972, 5-43733, and 5-345835. Many porous bodies of ceramicand metallic materials, rather than the resin materials, have beenproposed as water-resistant mold materials for pressure casting.

The pressure casting contributes to an increase in the productivitybecause the rate at which the slurry is deposited by the pressurecasting is much higher than the gypsum slip casting due to directpressurization of the slurry as described above. However, the directpressurization of the slurry requires the provision of a strong pipingstructure, a strong mold structure, and a strong press structure forcombining mold members (a molding space in a mold is usually formed bycombining a plurality of mold members), resulting in a huge costrequired for the molding facility.

The cost of the required molding facility is smaller for an arrangementin which no external pressure is applied to the slurry, as is the casewith the slip casting process using the gypsum mold. It is aneconomically better choice to use a water-resistant mold material ratherthan gypsum in order to increase the service life of a mold, and depositthe slurry mainly under capillary attractive forces of the moldmaterial, as is the case with the slip casting process using the gypsummold.

However, the above choice suffers large problems. Since thewater-resistant mold material is used, it does not provide moldreleasability of its own accord as with the gypsum molds. Japanesepatent publication No. 5-80324, for example, discloses an unsaturatedpolyester mold material having a self water absorption capability undercapillary attractive forces, but only describes, with respect to moldreleasability, the application of a gypsum spray to the surface of themold prior to a slip casting process and the use of heat radiation orhot air when removing the molded product from the mold. These attemptsto achieve mold releasability require respective facilities to removethe gypsum powder attached to the surface of the molded product in theformer arrangement and to generate the heat radiation or hot air in thelatter arrangement. Therefore, such facilities are as costly as thepressure casting facilities.

There has also been proposed a mold material such as resin-containinggypsum or gypsum which contains a water-insoluble filler, rather thanordinary gypsum. However, the water resistance of these special gypsummold materials is only slightly larger than the water resistance ofordinary gypsum, and the number of molded products that can be producedby one mold of such special gypsum mold materials ranges from 200 to300, which is slightly greater than with the gypsum molds.

One merit that is obtained when a back pressure is applied to the moldto release the molded product from the mold is that it allows moldedproducts to be produced in a successive slip casting process which hasnot been possible with the conventional gypsum molds. Specifically, thedeposition of a molded product is carried out in a gypsum mold byabsorbing water in a slurry under capillary attractive forces of themold. Consequently, when 1˜3 molded products are successively formed bya dry gypsum mold, the pores of the gypsum mold are filled with water,making it impossible to develop capillary attractive forces. Accordingto the customary practice, therefore, after 1˜3 molded products aresuccessively formed by a gypsum mold in daytime, the gypsum mold isdried almost completely at night, and then used for slip casting thenext morning. As a result, the productivity of the gypsum mold is low,and the cost of energy used to dry the gypsum mold is noticeably large.

If a water-resistant material rather than gypsum is developed, then itmaybe used as a mold material, and the shortcoming of poor moldreleasability due to its water resistance may be eliminated by using amechanism to apply a back pressure to supply water and air between themold and the molded product to release the molded product from the mold.Because water absorbed by the mold in the molding process can bedischarged by the above mechanism, capillary attractive forces can berecovered for successively molding molded products. However, even such awater-resistant material would suffer the following drawbacks:

Since capillary attractive forces cannot be produced when the pores ofthe mold are filled with water, a back pressure is exerted to the moldto remove the water from the mold. However, resistance to the passage ofair and water poses problems. Specifically, a mold which has largecapillary attractive forces and a high deposition rate has pores ofsmall diameter, and hence it is not easy to remove water from the pores.

When a back pressure is applied to the mold to release the moldedproduct therefrom, if a large amount of air were discharged, the moldedproduct would tend to be broken and damaged by the air. For smoothlyremoving the molded product from the mold, therefore, it is necessary tocreate a water film between the mold and the molded product. Such awater film can be formed relatively easily in the pressure castingprocess for the following reasons: Because the mold is not required tohave capillary attractive forces in casting cycles of the pressurecasting process, the mold is used substantially in a water-saturatedcondition, which signifies the suction of much more water upon slurrydeposition than a small amount of water discharged upon release of themolded product (therefore, it is necessary to discharge a considerableamount of water out of the mold upon slurry deposition). In the slipcasting which primarily employs capillary attractive forces to deposit aslurry, it is necessary to remove water from the pores of the mold inorder to produce capillary attractive forces, and hence the slip castingprocess has to be carried out under conditions to break the water filmwith ease. Using the mechanism to apply a back pressure for releasingthe molded product from the mold results in an increase in the costcompared with the gypsum slip casting.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a castingmethod which will provide excellent deposition capability and moldreleasability in a slip casting method that primarily employs capillaryattractive forces to deposit a slurry, without incurring as muchfacility cost as the known pressure casting process.

Another object of the present invention is to provide a slip castingmold material which can produce more molded products and has betterproductivity (deposition capability and mold releasability) than theconventional gypsum slip casting mold, and a method of manufacturingsuch a slip casting mold material.

The above objects can be achieved according to the invention by a methodof slip casting a powdery material with a slip casting mold having aself water absorption capability and a water absorption layer which issubstantially water resistant, comprising the steps of I) controllingthe water saturation percentage of the water absorption layer, II)pouring a slurry into the slip casting mold, III) depositing the slurryon the water absorption layer under a slip casting pressure whichcomprises a pressure selected from at least one of a) a slurry headpressure, b) a suction vacuum applied to the water absorption layer, andc) a pressure of at most 0.3 MPa applied directly to the slurry, and IV)releasing a deposited molded body from the slip casting mold.

The inventors have made detailed studies with respect to a process ofcontrolling the layer depositing capability and mold releasability of aslip casting mold for the purpose of accomplishing the above objects. Asa consequence, there is also provided in accordance with the presentinvention a method of manufacturing an open porous body for use in aslip casting mold for slip casting a powder material, comprising thesteps of: stirring a mixture of an epoxy compound having at least oneepoxy ring in one molecule, a hardener for reacting with the epoxycompound to harden the epoxy compound, a filler for developing selfwater absorption capability and mold releasability, and water into anO/W-type emulsion slurry; casting the emulsion slurry into a moldimpermeable to water; and hardening the emulsion slurry in the moldwhile containing the water. The open porous body can be used in a slipcasting mold which has self water absorption capability and moldreleasability.

There is also provided according to the invention a slip casting moldfor slip casting a powdery material, which uses the open porous body asa water absorption layer thereof.

Further objects, advantages and salient features of the invention willbecome apparent from the following detailed description which, whenconsidered in conjunction with the annexed drawings, describes presentlypreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing air grooves defined in an openporous body layer according to the present invention;

FIG. 2 is a cross-sectional view of a coarse porous layer having an airpipe and mounted on the reverse side of the open porous body layeraccording to the present invention;

FIG. 3 is a block diagram of successive steps in a slip casting methodaccording to the present invention;

FIG. 4 is a schematic view of a cassette-type slip casting moldaccording to the present invention, with air grooves defined in an openporous body layer;

FIG. 5 is a schematic view of a cassette-type slip casting moldaccording to the present invention, with air grooves defined in acassette case; and

FIG. 6 is a cross-sectional view of an internal structure of a slipcasting mold according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The presently preferred embodiments of the present invention will bedescribed below with reference to the accompanying drawings and tables.

The step of controlling the water saturation percentage of a waterabsorption layer in a method of slip casting a powdery material willfirst be described below.

Table 1 shows the relationship between the mold water saturationpercentage, the deposition rate constant k, and the molded body watercontent percentage of a molded body at the time a slurry for molding apiece of sanitary earthenware is poured into an epoxy resin mold testpiece. The mold water saturation percentage is 100% when all the moldpores are filled with water. The deposition rate constant k iscalculated according to the equation: k=L² /T where T is the timerequired to deposit a layer to a thickness of about 8 mm in the mold,and L is the measured thickness of the deposited layer. The molded bodywater content percentage is a water content percentage with respect to adry reference immediately after the layer was deposited to a thicknessof about 8 mm in the mold.

                  TABLE 1                                                         ______________________________________                                        Mold water   Deposition rate                                                                          Molded body water                                     saturation   constant k content percentage                                    percentage (%)                                                                             (mm.sup.2 /100 sec)                                                                      (%, dry base)                                         ______________________________________                                        0.4          1.8        25.9                                                  9.5          1.9        26.0                                                  20.3         1.8        26.1                                                  31.5         2.0        25.8                                                  40.3         2.6        24.7                                                  50.8         2.8        24.1                                                  60.1         2.8        24.2                                                  70.9         2.5        24.8                                                  78.1         2.3        25.2                                                  81.0         1.2        26.9                                                  ______________________________________                                    

As can be seen from Table 1, the deposition rate constant k is thegreatest when the mold water saturation percentage is in the range of 30to 80%, and is lower in a dry state which has been considered to be agood condition for the gypsum slip casting. The molded body watercontent percentage may be considered as important a factor as thedeposition rate because mold materials with smaller water contentpercentages are more resistant to deformation upon removal of the moldedproduct and are subject to smaller dry shrinkage after removal of themolded product. From this standpoint, it is preferable to control themold water saturation to range from 30 to 80%.

A slurry is poured into the mold whose water saturation percentage hasthus been controlled, and then the step of depositing a layer in themold is carried out.

In the method of slip casting a powdery material according to thepresent invention, capillary attractive forces of the mold are primarilyemployed to deposit a layer in the mold. However, another pressure mayalternatively or additionally be employed as a slip casting pressure.For example, since the head pressure of the slurry is usually used topour the slurry into the mold, the head pressure may conveniently beused as the slip casting pressure.

In a slip casting process using an ordinary gypsum mold, since thegypsum has relatively small strength and suffers cracks even when it isslightly deformed, the head height is limited to at most about 0.4 m(the slurry head height indicates the distance from the uppermostportion of the molded product to the upper surface of the slurry).

In a preferred embodiment according to the present invention, since aresin mold of a greater strength is used, the head height can beincreased preferably to 0.4 m or more and more preferably to 0.6 m ormore.

The increased head height results in such an advantage that it canincrease the deposition rate when applied as a slip casting pressure.However, any practical slurry head height, no matter how high it may be,is smaller than the capillary attractive forces of the mold. Thegreatest merit of the increased head height is to be able to reduce themolded product water content percentage, and manifests itself accordingto the present invention as compared with the gypsum slip casting.

If a mechanism for passing air and water is used to control the watersaturation percentage of the mold material and release the moldedproduct from the mold, as described later on, then the mechanism may beemployed to evacuate the mold under a vacuum suction pressure which maybe used as a slip casting pressure. The vacuum suction pressure may alsobe used not only in the step of depositing a layer, but also in the stepof pouring the slurry and the step of compacting the deposited layer, asdescribed later on. If the vacuum suction pressure is used in the stepof pouring the slurry, then since air is removed from the molding spacein the mold, the slurry can be poured into the mold at an increasedspeed, and pins are less liable to exist in the molded product. If thevacuum suction pressure is used in the step of compacting the depositedlayer, then the deposited layer is compacted at an increased speed.

If the mold is evacuated during the step of depositing a layer in themold, however, then the surface of the molded product may possibly bepeeled off upon removal from the mold depending on the type of thematerial of the molded product and the conditions under which the moldedproduct is formed. If the material of the molded product contains manyfine particles, then the surface of the molded product is more likely tobe peeled off.

The surface of the molded product may be prevented from being peeled offby a process of not evacuating the mold from a time near the end of thedeposition step, rather than evacuating the mold throughout thedeposition time of the deposition step. If such a process is employed,then it is preferable to evacuate the mold during a time selected in theperiod from the start of the deposition step to 80% of the time of thedeposition step. For example, if the deposition time is 30 minutes, thenthe time during which to evacuate the mold may be selected from 0 minuteto 24 minutes, or 0 minute to 20 minutes, or 2 minutes to 20 minuteswhere 0 minute is the start time of the deposition step. Another processof preventing the surface of the molded product from being peeled off isto reduce the suction vacuum as the deposition time progresses in thedeposition step. For example, if the deposition time is 60 minutes, thenthe suction vacuum may be reduced such that it is 0.08 MPa from 0 minuteto 30 minutes, 0.04 MPa from 30 minute to 50 minutes, and 0.01 MPa from50 minutes to 60 minutes, where 0 minute is the start time of thedeposition step.

The above two processes may be combined with each other. For example, ifthe deposition time is 50 minutes, then, then the suction vacuum may be0.06 MPa from 0 minute to 30 minutes and 0.02 MPa from 30 minute to 40minutes, and the mold is not evacuated from 40 minutes to 50 minuteswhere 0 minute is the start time of the deposition step.

The slip casting pressure in the slip casting method according to thepresent invention may be produced by a piston or a pump for directlypressurizing the slurry, as with the pressure casting. However, it isnot preferable to directly pressurize the slurry because the mold andthe casting machine will have to be of a rugged construction. If theslurry is nevertheless to be directly pressurized, then the pressureapplied to the slurry should be 0.3 MPa or less.

After the slurry has been deposited to the point where the moldedproduct has a predetermined thickness, the molded product is releasedfrom the mold. The molded product may be released from the mold byeither a natural releasing process in which the molded product isreleased from the mold naturally of its own accord or a water filmreleasing process in which the molded product is released from the moldby water and air supplied to a boundary surface between the mold and themolded product under a back pressure applied to the mold. The naturalreleasing process requires use of a mold material which provides selfmold releasability while substantially maintaining water resistance, andwill be described later on. The water film releasing process is requiredto discharge water and air uniformly from the surface of the mold.Unless a water film is created in the boundary surface between the moldand the molded product, the molded product will be blown off by the air.The above preferable range from 30 to 80% for the water saturationpercentage prior to the pouring the slurry into the mold is a rangeappropriate for smoothly releasing the molded product from the mold withthe water film (The water saturation percentage may be 80% or more,e.g., 100%, for releasing the molded product from the mold with thewater film, but the deposition rate is lower with such water saturationpercentage).

There are two types of slip casting processes, i.e., a solid castingprocess in which water is absorbed by the mold from opposite sides ofthe molded product (also referred to as a core casting process, with aportion of the molded product thus produced being referred to as a coreportion), and a drain casting process in which water is absorbed by themold from one side of the molded product and an excessive slurry isdrained after a layer is deposited to a predetermined thickness (alsoreferred to as a single-sided casting process, with a portion of themolded product thus produced being referred to as a single-sidedportion). Most pieces of sanitary earthenware include both core andsingle-sided portions in a molded body.

The method according to the present invention is applicable to both thesolid casting process and the drain casting process. However, if themethod according to the present invention is applied to the draincasting process, then it is necessary to add the step of draining anexcessive slurry and the step of compacting the deposited layer bylowering the water content percentage of a slurry drained surface of thedeposited layer to increase the hardness thereof, between the depositionstep and the mold release step.

In the step of draining an excessive slurry, a slurry draining air holeis defined in the mold in communication with the molding space, and airis delivered under pressure into the molding space through the slurrydraining air hole to discharge the excessive slurry (through a dischargeport which is usually the inlet port through which the slurry has beenintroduced into the mold). In the next step of compacting the depositedlayer, water in the slurry drained surface of the deposited layer flowsthrough the molded product into the mold material under capillaryattractive forces of the mold even when the molded product is left tostand. For shortening the time required for compacting the depositedlayer, it is preferable to introduce air under pressure into a slurrydraining space (usually through the slurry draining air hole).

The higher the pressure applied to air introduced into the slurrydraining space for compacting the deposited layer, the greater the speedat which the water content percentage of the slurry drained surface ofthe deposited layer drops. In the conventional process using the gypsummold, since the mold would otherwise be broken or the molded productwould otherwise crack, an upper limit for the air pressure applied inthe step of compacting the deposited layer has been about 0.005 MPa.According to the present invention, since the mechanism for releasingthe molded product from the mold is different from that used in thegypsum slip casting process and the resin mold of a greater strengththan the gypsum mold is used in the preferred embodiment, the pressureapplied to compact the deposited layer can be increased, and shouldpreferably range from 0.005 MPa to 0.4 MPa, and more preferably rangefrom 0.007 MPa to 0.1 MPa.

The water maybe caused to flow in the step of compacting the depositedlayer by a suction vacuum applied to evacuate the mold in combinationwith the air introduced under pressure into the slurry draining space.If the mold is evacuated during the step of compacting the depositedlayer in the mold, however, then the surface of the molded product maypossibly be peeled off upon removal from the mold depending on the typeof the material of the molded product and the conditions in which themolded product is formed. If the material of the molded product containsmany fine particles, then the surface of the molded product is morelikely to be peeled off.

The surface of the molded product may be prevented from being peeled offby a process of not evacuating the mold from a time near the end of thecompacting step, rather than evacuating the mold throughout thecompacting time of the compacting step. If such a process is employed,then it is preferable to evacuate the mold during a time selected in theperiod from the start of the compacting step to 80% of the time of thecompacting step. For example, if the compacting time is 10 minutes, thenthe time during which to evacuate the mold may be selected from 0 minuteto 8 minutes, or 0 minute to 5 minutes, or 2 minutes to 7 minutes where0 minute is the start time of the compacting step.

Another process of preventing the surface of the molded product frombeing peeled off is to reduce the suction vacuum as the compacting timeprogresses in the compacting step. For example, if the compacting timeis 15 minutes, then the suction vacuum may be reduced such that it is0.08 MPa from 0 minute to 10 minutes, 0.04 MPa from 10 minute to 13minutes, and 0.01 MPa from 13 minutes to 15 minutes where 0 minute isthe start time of the compacting step.

The above two processes may be combined with each other. For example, ifthe compacting time is 20 minutes, then, then the suction vacuum may be0.06 MPa from 0 minute to 10 minutes and 0.02 MPa from 10 minute to 15minutes, and the mold is not evacuated from 15 minutes to 20 minuteswhere 0 minute is the start time of the compacting step.

If the mold releasing step of removing a molded product from a moldunder a back pressure applied to the mold is employed, water and air aredischarged from the molding surface at the end of the removal of themolded product from the mold. Therefore, if the end of the removal ofthe molded product from the mold is followed by the step of controllingthe water saturation percentage of a water absorption layer, then thesteps are carried out smoothly one after another, making it possible tocontrol molded product releasing conditions for equalizing the watersaturation percentage of the mold at the end of the removal of themolded product from the mold to the appropriate water saturationpercentage of the mold at the time of pouring the slurry into the mold.

The various steps of the slip casting method according to the presentinvention have been described above. Now, a process of controlling thewater saturation percentage of the water absorption layer will bedescribed below.

Since the water saturation percentage of the water absorption layer isin the range of 30 to 80% at the time of pouring the slurry into themold, it is preferable to adjust the water saturation percentage of thewater absorption layer into the above range.

For example, if the amount of water absorbed from the slurry in aprevious casting cycle occupies a considerable proportion of the volumeof the water absorption layer, then it is necessary to dehydrate thewater absorption layer before the slurry is poured into the mold. Statedotherwise, if a large amount of water is discharged from the mold whenthe molded produced is released from the mold under a back pressureapplied thereto, then it is necessary to supply water to the waterabsorption layer before the slurry is poured into the mold.

The water saturation percentage of the water absorption layer may becontrolled by either introducing water to discharge air or introducingwater to discharge water. In addition, if the water saturationpercentage of the water absorption layer is higher than a desired targetvalue, then water may be introduced into the water absorption layer tofurther increase the water saturation percentage thereof, and thereafterair may be introduced to lower the water saturation percentage down tothe target value. This latter process is relied upon when the watercontent percentage of the water absorption layer is irregular uponremoval of the molded product from the mold because it is not possibleto deposit a uniform layer in the mold and to form a water film uponremoval of the molded product from the mold. In this case, water isintroduced to make uniform the water content percentage, and then air isintroduced to lower the water saturation percentage down to the targetvalue. With this process, the molding surface and air grooves (describedlater) can be cleaned to increase the service life of the mold, i.e.,the number of molded products that can be produced by the mold.

The water may often contain various impurities such as ions. If thewater contains those various impurities, then the above process ofintroducing water into the water absorption layer to increase the watersaturation percentage thereof, and then introducing air to lower thewater saturation percentage down to the target value is not preferableas it will cause clogging of the mold.

In such a case, the introduction of water into the mold should beavoided as much as possible. If water has to be introduced periodically(e.g., once a week or a month) to clean the air grooves, then water fromwhich impurities have been removed by various filters should beintroduced into the mold.

A process of introducing air or water into the water absorption layerwill be described below. It is preferable to introduce air or water intothe water absorption layer by providing air and water passing means forpassing air and water into the water absorption layer, and introducingair and water into the mold through the air and water passing meansunder a back pressure.

The air and water passing means is also effective in evacuating the moldto increase the deposition rate at the time a layer is deposited in themold and also in applying a back pressure to the mold to release themolded product from the mold with a water film, in addition tocontrolling the water saturation percentage.

The air and water passing means may comprise air grooves defined withinthe water absorption layer or in the reverse side of the waterabsorption layer for passing air and water therethrough. The air groovesmay be defined at constant intervals substantially parallel to themolding surface, as shown in FIG. 1, or at constant intervalssubstantially perpendicularly to the molding surface, or may bepositioned in various patterns in the water absorption layer, so thatair and water can be discharged substantially uniformly from the moldingsurface when a back pressure is applied to the mold. The air grooves areconnected into one or more main air grooves which are connected to apipe extending out of the mold for passing air and water therethrough.

Furthermore, the air and water passing means may comprise a coarseporous layer disposed on the reverse side of the water absorption layerand having an air pipe extending out of the mold for passing water andair, as shown in FIG. 2. In this arrangement, when the air pipe ispressurized, the pressure in the coarse porous layer tends to berelatively uniform because the pores thereof have large diameters, forthereby discharging water and air relatively uniformly from the moldingsurface. One air pipe may be provided per mold, or if the pressure inthe coarse porous layer is not uniform with one air pipe, then aplurality of air pipes may be provided per mold. These air pipes extendout of the mold for passing air and water therethrough.

The water absorption layer which is substantially resistant to waterthat is used in the present invention will be described below. The term"resistant to water" means not using a mold material which achieves moldreleasability by dissolving its surface, as is the case with a gypsummold. Mold materials which are resistant to water include a resin moldmaterial, a metallic mold material, a ceramic mold material, etc. Forexample, since a mold for manufacturing a product having a complexshape, such as sanitary earthenware, should preferably be a mold thatcan be formed by pouring a mold material, such a mold should preferablya resin mold. Resin molds include an epoxy mold, an acrylic mold, anunsaturated polyester mold, etc. In view of the viscosity of a resin,the length of a pot life, etc., an epoxy mold is relatively easy to use.

The water absorption layer has its self water absorption capabilitydeveloped by capillary attractive forces of a mold material which is anopen porous body. An open porous body for making a metallic mold or aceramic mold may be produced by sintering a metallic powder or a ceramicpowder, so that interstices between sintered particles will be utilizedas pores. For making an epoxy mold, for example, an epoxy resin(including a hardener), water, and a filler are mixed into an emulsionslurry of the O/W type (an oil phase is dispersed in a water phase whichis a continuous phase), and after the emulsion slurry is hardened, poresare formed in the water phase which is a continuous phase.

For applying the casting method according to the present invention to anindustrial production line, the steps of the method have their owncharacteristic operations. For example, a large amount of water ispossibly discharged from the mold in the step of controlling the watersaturation percentage of the water absorption layer and the step ofreleasing the molded product from the mold with the water film, anddedicated devices are required for the introduction of the slurry andthe vacuum suction. The cost of equipment may be reduced by associatingthe steps with respective stations, providing a facility for processingdischarged water in the steps of discharging a large amount of water,and providing dedicated devices only in the stations of correspondingsteps, rather than for all molds. In such an arrangement, since acarriage device is needed to move the mold between stations, whether thetype in which the mold is movable or the type in which the mold is fixedshould be selected differs from case to case.

In the type in which the mold is movable, not all steps are required tobe carrird out in different stations. As shown in FIG. 3, stations maybe provided for respective blocks where some successive steps are puttogether.

If stations are provided for respective blocks, and a plurality of moldsare handled in one station, then the number of stations is reduced, butthe carriage device for the molds is complex.

If the disadvantage associated with a complex carriage device for themolds is too large, then it is preferable to use a system which handlesa single mold in one station. Such a system should preferably employ twostations, i.e., a station in which the slurry is poured into the moldand a layer is deposited in the mold (the slurry is discharged and thedeposited layer is compacted), and a station in which the moldedproduced is released from the mold. Controlling the water saturationpercentage is carried out in either one of the two stations (usually,the station in which the molded product is released from the mold).

Applications of the slip casting method according to the presentinvention are not limited to any specific fields. However, the slipcasting method according to the present invention is effectively appliedto the production of ceramic whiteware such as sanitary earthenware,fine ceramic products, and powder metallurgy products, for example.

A slip casting mold and a method of manufacturing an open porous bodyfor use in such a slip casting mold according to the present inventionwill be described below.

An epoxy compound used in the present invention has one or more epoxyrings in one molecule, is a liquid at normal temperature, and has a lowviscosity convenient for producing an emulsion slurry. The epoxycompound should preferably be a glycidyl epoxy resin, and morepreferably a bisphenol epoxy resin such as a bisphenol A epoxy resin, abisphenol F epoxy resin, a bisphenol AD epoxy resin, or the like.

A hardener for the epoxy compound should preferably be of polyamide,polyamine, modified polyamine, or a mixture thereof for producing anemulsion slurry of low viscosity. (The emulsion slurry of low viscosityis preferable because it can be introduced into every corner and creviceof the large and complex slip casting space of molds for forming largeand complex molded products.) Particularly preferable among thosehardeners is a polyamide hardener.

The development of self water absorption capability and moldreleasability with a filler, which is the most important aspect of thepresent invention, will be described below. The self water absorptioncapability and mold releasability can be developed with a filler byvarious means which can be combined with each other. With respect to theself water absorption capability, the ability of a mold to deposit theslurry is produced by capillary attractive forces of the mold material.Therefore, the question is how capillary attractive forces of the moldmaterial are developed by the filler. In this connection, it isimportant to note that the deposition characteristics of the slurrymaterial are affected by not only the capillary attractive forces of themold material but also the resistance to passage of water. Theresistance to passage of water is roughly divided into a resistanceimposed by the deposited layer and a resistance imposed by the mold(strictly, from the molding surface of the mold to the tip end of thewater saturated portion thereof). A mold which provides large capillaryattractive forces has a small pore diameter. However, since a mold whichhas a small pore diameter presents a large resistance to passage ofwater, a mold which provides large capillary attractive forces may notnecessarily have an excellent self water absorption capability. It isnecessary for a mold to have a balance between capillary attractiveforces and a resistance imposed by the mold material to passage ofwater. Inasmuch as the resistance imposed by the mold material topassage of water affects the deposition rate in combination with theresistance imposed by the deposited layer to passage of water, optimumproperties of the mold cannot be determined solely based on the moldmaterial, but should be determined in combination with various depositedlayers.

For slip casting a molded product with a completely dry mold, if theaverage water content percentage of the deposited layer is constant andalso the mold absorbs water uniformly, then the ratio between theresistance imposed by the deposited layer to passage of water and theresistance imposed by the mold material to passage of water is constantat all times. In the slip casting method according to the presentinvention, it is sometimes preferable to slip cast a molded product witha mold having a considerably high water saturation percentage. In such acase, the ratio between the resistance imposed by the deposited layer topassage of water and the resistance imposed by the mold material topassage of water varies as the slurry is deposited, and hence it isnecessary to take into account the water saturation percentage of themold upon start of the deposition of the slurry and the deposition time(the amount of the deposited material).

In view of the above analysis, the inventors have conducted experimentson various materials for slip casting sanitary earthenware under variousdifferent casting conditions, and found that the following conditionsshould be satisfied in order to manufacture a slip casting mold whichprovides an industrially effective deposition rate:

If the hardener mainly made of polyamide is used, then the filler shouldpreferably have an average particle diameter ranging from 0.3 μm to 8μm. The filler may be of any material insofar as it can be bonded by anepoxy resin and its grain size can be controlled. For example, thefiller may be of a powder of siliceous stone or a powder of siliceoussand. The average particle diameter is defined as a particle diameterrepresenting a 50% cumulative volume according to a volumetricreference. If the average particular diameter were smaller than 0.3 μmor greater than 8 μm, then insufficient capillary attractive forceswould be developed under industrial casting conditions.

If the hardener is made of a product produced by a reaction betweenchain-like fatty primary polyamine and glycidyl ether having two or moreglycidyl groups in one molecule, then the filler should preferably havean average particle diameter ranging from 1 μm to 20 μm. If the averageparticular diameter were smaller than 1 μm or greater than 20 μm, theninsufficient capillary attractive forces would be developed underindustrial casting conditions. The filler may be of any material insofaras it can be bonded by an epoxy resin and its grain size can becontrolled. For example, the filler may be of a powder of siliceousstone or a powder of siliceous sand. The chain-like fatty primarypolyamine is preferably represented by H₂ N[(CH₂)₂ NH]_(n) (CH₂)₂ NH₂with amino groups on opposite ends of the molecule, and more preferablycomprises diethylenetriamine, triethylenetetramine,tetraethylenepentamine, or pentaethylenehexamine. The glycidyl etherhaving two or more glycidyl groups in one molecule preferably comprisesneopentyl glycol glycidyl ether having two glycidyl groups in onemolecule, 1,6 hexanediol glycidyl ether, ethylene glycol glycidyl ether,bisphenol A glycidyl ether, or trimethylolpropane triglycidyl etherhaving three glycidyl groups in one molecule. In the reaction betweenchain-like fatty primary polyamine and glycidyl ether having two or moreglycidyl groups in one molecule, if m amino groups per molecule of thechain-like fatty primary polyamine are to be changed into imino groups,then the preferable rate of progress of the reaction which isrepresented by the number m of amino groups is in the range of 0.1≦m≦1.5(if imino groups are to be further reacted with the glycidyl groups,then the number of such imino groups is also counted as m). If thenumber m were smaller than 0.1, then insufficient capillary attractiveforces would be developed under industrial casting conditions. If thenumber m were greater than 1.5, then the product produced by thereaction between chain-like fatty primary polyamine and glycidyl etherhaving two or more glycidyl groups in one molecule would be too viscousto handle with ease.

If the hardener is primarily composed of 1˜5 wt % of a product producedby a reaction between monomer fatty acid and chain-like fatty primarypolyamine and 99˜95 wt % of a product produced by a reaction betweenpolymer fatty acid and chain-like fatty primary polyamine, then thefiller should preferably have an average particle diameter ranging from1 μm to 20 μm. If the average particular diameter were smaller than 1 μmor greater than 20 μm, then insufficient capillary attractive forceswould be developed under industrial casting conditions. The filler maybe of any material insofar as it can be bonded by an epoxy resin and itsgrain size can be controlled. For example, the filler may be of a powderof siliceous stone or a powder of siliceous sand. The monomer fatty acidis preferably mainly composed of oleic acid, linolic acid, or erucicacid. The chain-like fatty primary polyamine is preferably representedby H₂ N[(CH₂)₂ NH]_(n) (CH₂)₂ NH₂ with amino groups on opposite ends ofthe molecule, and more preferably comprises diethylenetriamine,triethylenetetramine, tetraethylenepentamine, or pentaethylenehexamine.The polymer fatty acid is preferably mainly composed of dimer acid. Ifthe proportion of the product produced by the reaction between monomerfatty acid and chain-like fatty primary polyamine were smaller than 1 wt% or greater than 5 wt %, then insufficient capillary attractive forceswould be developed under industrial casting conditions. If theproportion of the product produced by the reaction between polymer fattyacid and chain-like fatty primary polyamine were greater than 99 wt % orsmaller than 95 wt %, then insufficient capillary attractive forceswould be developed under industrial casting conditions.

The various preferable means for causing an open porous body to developa self water absorption capability with a filler have been describedabove according to the type of the filler. Now, the development of moldreleasability with a filler will be described below. The development ofmold releasability with a filler can be classified into two largecategories. In the first category, a mold material itself is given moldreleasability by the action of a filler. According to one preferableexample of this category, the filler is primarily composed of aluminumhydroxide. The filler may be entirely composed of aluminum hydroxide, ormay be combined with another filler. If the filler is combined withanother filler, then the proportion of aluminum hydroxide in thecombination of fillers should preferably be 30 vol. % or more.

According to another preferable example of this category, the filler isprimarily composed of a hydraulic material. In this example, a moldmaterial is made of an emulsion slurry of the O/W type. Since thehydraulic material of the filler is hardened by water of the continuousphase, an open porous body can easily be produced. The filler may becomposed of a hydraulic material in its entirety, or may be combinedwith another filler. If the filler is combined with another filler, thenthe proportion of the hydraulic material in the combination of fillersshould preferably be 30 vol. % or more. The hydraulic material ispreferably alumina cement, Portland cement, mixed cement composedprimarily of Portland cement, α hemihydrate gypsum, or β hemihydrategypsum.

Another advantage which is obtained by using a hydraulic material as amain component of the filler is that the grain size distribution of thefiller can be controlled by the crystal of fine particles generated by ahydrating reaction. Therefore, using a hydraulic material as a maincomponent of the filler can be effective to develop capillary attractiveforces of an open porous body. If a hydraulic material is used as amaterial of the filler, then various additives including a hardeningaccelerator, a hardening retarder, an expanding agent, an AE agent, etc.which can be used in combination with various hydraulic materials may beadded.

If a hydraulic material is used as a material of the filler, then twofactors, i.e., a curing reaction of a resin and a hydrating reaction ofthe hydraulic material, are involved in a hardening reaction of anemulsion slurry, and a balance is required to be achieved between theabove two factors. With respect the curing reaction of a resin, thepreferable hardening temperature (the atmospheric temperature of acuring chamber) ranges from 20 to 50° C., which is a normal temperaturerange for curing an epoxy resin. If a hydraulic material is used as amaterial of the filler, then since the deposition rate may be greater atlower curing temperatures, the preferable hardening temperature rangesfrom -20 to 50° C. If the curing temperature is set to 20° C. or below,it is preferable to cure the resin at 20° C. or below in a primarycuring process and then cure the resin at 20 to 50° C. in a secondarycuring process for post-curing of the resin. For setting the curingtemperature to a lower temperature, it is necessary to not only controlthe temperature of the curing chamber, but also cool the materials used.Cooling the hydraulic material before it is mixed with other materialsis often effective to increase the deposition rate in particular.

In the second category of the development of mold releasability with afiller, the ability of an open porous body to pass a fluid therethroughis employed. The ability of an open porous body to pass a fluidtherethrough is the ability of a mold of an open porous body to passwater and air therethrough for releasing a molded product from the moldwith the water and air supplied to a boundary surface between the moldand the molded product under a back pressure applied to the mold. Oneproblem which is encountered is that if capillary attractive forces ofthe mold are used to deposit a layer in the mold, then reducing thediameter of pores of the mold for increasing the capillary attractiveforces also reduces the ability of the open porous body to pass a fluidtherethrough. To solve this problem, the grain size distribution of thefiller may be selected to be as sharp as possible, i.e., the filler maybe of uniform particle diameters. Inasmuch as it is highly industriallydifficult to make uniform the diameters of all particles, there is apreferable grain size distribution that can be controlled industrially,as follows:

Generally, the grain size distribution of a powder is expressed by aRosin-Rammler's distribution. According to the Rosin-Rammler'sdistribution, a particle diameter corresponding to 36.8% by integratedsieved volume (which does not mean actual sieving, but means that volume% of particles having diameters greater than the particle diameter is36.8%) is referred to as an absolute size constant, and recognized as acentral particle diameter. In order to increase the ability to pass afluid without substantially affecting the deposition rate, it ispreferable to make sharp the grain size distribution of fine particlesin particular, and the integrated sieve volume of particle diameterswhich are 1/4 of the absolute size constant may be selected not toexceed 30%. With respect to the grain size distribution of coarseparticles, the ability to pass a fluid can be increased by adding asmall amount of coarse particles (the grain size distribution has two ormore peaks, i.e., a peak provided by the central fine particles and apeak provided by the small amount of coarse particles). Adding the smallamount of coarse particles is also effective to slightly suppress theoccurrence of a dilatancy phenomenon (described later on). The fillermay be of any material insofar as it can be bonded by an epoxy resin andits grain size can be controlled. For example, the filler may be of apowder of siliceous stone or a powder of siliceous sand.

A first method of preventing the emulsion slurry from exhibitingdilatancy is to add a dilatancy reducing agent as a material of theemulsion slurry. Preferable dilatancy reducing agents include variousnonionic surface active agents, cationic surface active agents, anionicsurface active agents, ampholytic surface active agents, organicsolvents such as methanol, ethanol, isobutyl alcohol, acetone, etc.,polymeric electrolytes such as carboxyl methyl cellulose sodium salt,methyl cellulose sodium salt, etc., and polymeric materials such aspolyethylene oxide which can be dispersed in water to impart thixotropy.

A second method of preventing the emulsion slurry from exhibitingdilatancy is to mix and stir an epoxy compound and water, then add afiller to the mixture and mix and stir the mixed materials, andthereafter add a hardener to the mixture and mix and stir the mixedmaterials.

The epoxy compound, the hardener, and the filler for developing selfwater absorption capability and mold releasability, which are used asmain materials of the emulsion slurry according to the present inventionhave been described above. To these materials, there may also be added areactive diluting agent such as butyl glycidyl ether, aryl glycidylether, styrene oxide, phenyl glycidyl ether, cresyl glycidyl ether,ethylene glycol glycidyl ether, neopentyl glycol glycidyl ether, 1,6hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, or thelike, a hardening accelerator such as benzyldimethylamine,2,4,6-tris(dimethylaminomethyl)phenol,2,4,6-tris(dimethylaminomethyl)phenol tri-2-ethylhexylate, or the like,a soluble salt such as potassium chloride, sodium chloride, zincchloride, calcium chloride, barium chloride, titanium chloride, ironchloride, nickel chloride, magnesium chloride, aluminum sulfate, zincsulfate, cobalt sulfate, aluminumammoniumsulfate,aluminumpotassiumsulfate, potassium sulfate, cobalt sulfate, ironsulfate, copper sulfate, sodium sulfate, nickel sulfate, magnesiumsulfate, manganese sulfate, sodium hydroxide, potassium hydroxide,calcium hydroxide, or the like, a debubblizer, a coloring agent, asurface active agent, and the like.

The open porous body for use in a slip casting mold for slip casting apowdery material has been described above. A slip casting mold whichincorporates the open porous body will be described below. The openporous body serves as a molding surface of the slip casting mold. Sincethe slip casting process which employs the slip casting mold accordingto the present invention is carried out under low pressures, the slipcasting mold does not require substantial strength. Therefore, majorcomponents of the slip casting mold may be composed of the open porousbody (whose strength is lower than the strength of a body which is notporous), and the slip casting mold is of a simple structure and can bemanufactured inexpensively.

However, a backing layer may be mounted on the reverse side of the moldwhich is opposite to the molding surface thereof. The backing layeroffers the following advantages: (1) The mold is made strong to provideagainst damage though the slip casting process is carried out under lowpressures. (2) The open porous body layer can be made as thin aspossible and hence is allowed to have uniform properties. If air groovesare defined in the mold, then since the distance from the air grooves tothe reverse side of the mold is reduced, the amount of water and airsupplied to mold portions which have nothing to do with releasing themolded product from the mold is reduced, thereby improving moldreleasability. The backing layer may be made of any materials, but caneasily be manufactured if it is made by solidifying a flowable material.For example, the backing layer may be made of plastic (whoseconstituents may all be organic, or which may contain a considerableproportion of an inorganic filler), or a hydraulic material such asconcrete, mortar, or the like. A reinforcing layer such as an iron framemay be mounted on the mold outwardly of the backing layer.

The backing layer and the open porous body layer may be separatelyproduced and bonded to each other. Alternatively, one of the backinglayer and the open porous body layer may be produced first, and after anadhesive is coated on a mating surface thereof, the other layer may bepoured onto the layer which has been produced first. If the other layerwhich is poured subsequently has a bonding capability with respect tothe layer which has been produced first, then the adhesive is notrequired to be coated on the mating surface.

The mold material which employs the open porous body according to thepresent invention is characterized by good mold releasability. Thedevelopment of mold releasability can be classified into two largecategories. In the first category, the mold material itself is givenmold releasability. In the second category, mold releasability is basedon the excellent ability of the open porous body to pass a fluidtherethrough under a back pressure applied to the mold. If a moldmaterial in the second category is used, then the open porous body isrequired to have air and water passing means. If a mold material in thefirst category is used, then it does not necessarily need any air andwater passing means. However, if mold releasability is to be furtherincreased or the open porous body is to be evacuated to increase thedeposition rate during the deposition process, then a mold material inthe first category may be combined with air and water passing means.

Air and water passing means for passing air and water into the openporous body may comprise air grooves defined inside or in the reverseside of the open porous body for introducing air and water through theair grooves or evacuating the open porous body through the air grooves.The air grooves may be arranged at constant intervals substantiallyparallel to the molding surface as shown in FIG. 1, or at constantintervals substantially perpendicular to the molding surface, or mayotherwise be arranged in various patterns in the open porous body, sothat when air under pressure is supplied to the open porous body, waterand air are discharged substantially uniformly from the molding surfacethrough the air grooves. The air grooves are connected into one or moremain air grooves which are connected to a pipe extending out of the moldfor pressurizing or evacuating the open porous body.

Another air and water passing means for passing air and water into theopen porous body may comprise a coarse porous layer disposed on thereverse side of the open porous body layer and having an air pipeextending out of the mold for passing water and air, as shown in FIG. 2.In this arrangement, when the air pipe is pressurized, the pressure inthe coarse porous layer tends to be relatively uniform because the poresthereof have large diameters, for thereby discharging water and airrelatively uniformly from the molding surface for removing the moldedproduct from the mold. The coarse porous layer preferably has an averagepore diameter of 100 μm for making uniform the pressure in the coarseporous layer. One air pipe may be provided per mold, or if the pressurein the coarse porous layer is not uniform with one air pipe, then aplurality of air pipes may be provided per mold. These air pipes extendout of the mold for pressurizing or evacuating the open porous body.

The coarse porous layer may be made of any materials insofar as they arestrong enough not to be damaged when pressurized. For example, thecoarse porous layer may be made of a material produced by mixing aliquid resin and a powder having an average particle diameter rangingfrom 0.1 to 5.0 mm at a ratio of 15˜50:100 and then curing the mixture.

The open porous body layer and the coarse porous layer may be separatelyproduced and bonded to each other. Alternatively, one of the open porousbody layer and the coarse porous layer may be produced first, and afteran adhesive is coated on a mating surface thereof, the other layer maybe poured onto the layer which has been produced first. If the otherlayer which is poured subsequently has a bonding capability with respectto the layer which has been produced first, then the adhesive is notrequired to be coated on the mating surface. When the open porous bodylayer and the coarse porous layer are joined to each other, they shouldallow air and water to pass between them, unlike the joint between thebacking layer and the open porous body layer. If an adhesive layer whichis not permeable to air and water is provided between the open porousbody layer and the coarse porous layer, then the adhesive layer shouldpartly cover the mating surface as in a grid-like pattern to leavesurface portions for passing air and water therethrough.

The air grooves and the coarse porous layer have been described above asthe air and water passing means for passing air and water to the openporous body layer. The air grooves or the coarse porous layer isrequired to be provided with the mold. To eliminate such a moldstructure, a cassette case may be detachably mounted on the reverse sideof the open porous body layer.

The cassette case is used semipermanently, and when the open porous bodylayer can no longer be used due to clogging, it is discarded, and a newopen porous body layer is set in the cassette case. Air and waterpassing means for passing air and water to the open porous body layer ofa slip casting mold of this structure may comprise air grooves disposedin a boundary surface between the open porous body layer and thecassette case. The air grooves may be defined in either the open porousbody layer as shown in FIG. 4, or in the cassette case as shown in FIG.5. The term "air grooves" used herein represents a space for passingwater and air therethrough. Therefore, the air grooves need not bedefined as shown in FIGS. 4 and 5, but may comprise a gap between thecassette case and the open porous body layer. In FIGS. 4 and 5, the openporous body layer is thinner at a mating surface of the mold for thefollowing reasons: When molds are combined and pressed to form a moldingspace therein, the mating surfaces are subjected to forces. The openporous body layer which is low in strength is thinner at the matingsurface to avoid damage from those forces.

In the slip casting mold of this structure, the cassette case and theopen porous body layer are required to be accurately, detachablycombined with each other for preventing water and air from leaking fromthe interface between the cassette case and the open porous body layerwhen the air grooves are pressurized. The cassette case and the openporous body layer may be detachably joined with each other by amechanical means such as bolts or a chemical means such as an adhesivewhich allows the open porous body layer to be peeled off forreplacement. The cassette case may be made of any materials such asresin, metal, or the like. A reinforcing layer such as an iron frame maybe mounted on the mold outwardly of the cassette case.

Applications of the slip casting mold according to the present inventionare not limited to any specific fields. However, the slip casting moldaccording to the present invention is effectively applied to theproduction of ceramic whiteware such as sanitary earthenware, fineceramic products, and powder metallurgy products, for example.

Each of specimens mixed at proportions shown in Tables 2 and 3, givenbelow, was placed in a stainless container, and intensively stirred for10 minutes at normal temperature, producing a uniform O/W-type emulsionslurry. The emulsion slurry was poured into a mold which is impermeableto water, covered so that no water would be evaporated, and left tostand in a room at 45° C. for 24 hours until it is hardened whilecontaining water. Some mixing and hardening conditions were differentfrom those described above as described in Remark 1 in Tables 2 and 3.

The hardened body was removed from the mold, and left to stand in adrier at 50° C. for 24 hours for evaporating water, producing an openporous body. The water is evaporated for the purpose of measuring theproperties of the open porous body. The evaporation of the water may notnecessarily be required for the actual production of a slip castingmold. The properties of the open porous body are shown in the testresults in Tables 2 and 3. The gypsum molds usually found in industrialuse have a deposition rate of about 1.5. Though experimenting methodsand results are omitted from illustration, all open porous bodies inSpecimens 1˜32 and Reference in Tables 2 and 3 were evaluated for waterresistance, and were confirmed as being substantially water-resistantcompared with the water-soluble gypsum molds.

In each of Specimens 1˜5, a powder of siliceous sand having an averageparticle diameter of about 2.5 μm was used as a filler, making a grainsize distribution sharp. In Reference, a powder of siliceous sand havingan average particle diameter of about 2.5 μm was used also as a filler,but the powder of siliceous sand was simply ground to make a grain sizedistribution broad.

In Specimens 1˜5, the deposition rate constants range from about 1.7 to1.9, and do not differ largely from each other. However, the amount ofwater passed by Specimens 1˜5 was at least three times the amount ofwater passed by Reference, and was greater as the grain sizedistribution was sharper. The amount of water passed by Specimen 5,whose grain size distribution had two peaks provided by the fine andcoarse particles, was greater.

In Specimens 6˜15, powders of siliceous sand having various particlediameters with a sharp grain size distribution were used as a filler.The smaller the average particle diameter, the greater the depositionrate constant, and the smaller the amount of passed water. The siliceoussands used in above Specimens have their grain size controllable andexamples of the filler which can be bonded by an adhesive.

To inspect effects of the shape of the filler, glass beads which isalmost fully spherical in shape were used in Specimens 16˜18. Thespherical filler has a sharp grain size distribution, but not so largean ability to pass water, as compared with the above filler. Thespherical filler, however, offers advantages in that since the viscosityof the emulsion slurry is low, the dilatancy phenomenon is less liableto occur, and mold releasability strength is low.

In Specimens 19˜22, a filler of aluminum hydroxide was used. As can beseen from the test results thereof, the open porous bodies were releasedwithout application of forces. In Specimens 23˜32, a filler of ahydraulic material was used. The open porous bodies in Specimens 23˜32had a self mold releasability as with those in Specimens 19˜22 in whicha filler of aluminum hydroxide was used.

    TABLE 2       - Specimen No.       Material Ref. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15       Epicoat 815 (*1) 445 445 445 445 445 445 345 390 470 520  448 200        Epomic R710 (*2)           450  225 450       Epicoat 807 (*3)               503 446       m.p. PCGE (*4)          40 69  50 23       Polyamide hardener A (*5) 160 160 160 160 160 160 166 170 172 176  165       160  185 160       Polymide L-55-3 (*6) 13 13 13 13 13 13 13       Hardener B (*7)            7 23  16 18       Hardener C (*8)           205   189       2.4.6-tris(diaminomethyl)phenol (*9) 14 14 14 14 14 14 13 14 14 14 13     11 12       Powder of siliceous sand (*10)       A 3004       B  3004       C   3004       D    3004       E     3004       F      3004       G          1980       H         2541     2449 2417 2471       I        3633       J       4158    2226       K            3003 2826       Glass beads A (*11)       Glass beads B (*12)       Aluminum hydroxide (*13)       Hemihydrate gypsum (*14)       Alumina cement (*15)       Portlant cement (*16)       Aluminum sulfite (*17)       Polyethylene oxide (*18)       0.6 0.6 0.8 0.9 0.8 0.8 0.8       Water 1230 1230 1230 1230 1230 1230 900 1050 1350 1500 1230 1230 1260     1410 1380 1440       Remark 1   *19 *19 *19 *19       *19 *19 *19       Test results       Bending strength (MPa) (*23) 6.0 6.5 6.3 6.7 6.7 7.1 10.3 8.2 5.1 3.9     6.7 7.0 7.3 6.9 7.0 7.1       Flexural modulus (MPa) (*23) 980 930 950 920 990 930 1350 1180 840 680       980 1050 1120 980 990 950       Deposition rate constant (0.01 mm.sup.2 /sec) ( 1.7 1.7 1.8 1.9 1.7     1.9 1.5 1.7 3.4 4.1 1.8 1.7 1.9 1.8 1.7 1.6       Amount of passed water (1000 mm.sup.3 /3 min.) ( 43 110 140 180 230     330 690 500 150 86 190 200 180 160 170 210       Mold releasability strength (0.01 MPa) ( 1.0 0.6 0.5 0.5 0.4 0.5 0.6     0.5 0.4 0.3 0.5 0.5 0.5 0.5 0.4 0.5       Emulsion slurry viscosity (mPa.sec) (* 5700 2300 2500 2000 2200 1800     5900 4200 1600 1100 2200 2000 1600 2200 1800 1700       Remark 2     *28     The unit for specimens is 0.001 kg.

    TABLE 3       - Specimen No.       Material 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32       Epicoat 815 (*1) 445  445 445 499 445 415 111 103 722 600 589 493 589     429 493 343               4 2       Epomic R710 (*2)         400       Epicoat 807 (*3)       m.p. PCGE (*4)  45       Polyamide hardener A (*5) 160 173 160 173 176 173 161 413 413 271 222     218 182 222 159 182 127       Polymide L-55-3 (*6) 13  13  20       Hardener B (*7)       Hardener C (*8)       2.4.6-tris(diaminomethyl)phenol (*9) 14 14 12 14 12 14 13 33  17 18 18       15 14 13 15 10       Powder of siliceous sand (*10)       A      133    133    108  546 634             5    5    9       B       C       D       E       F       155              8       G       H       I       J       K       Glass beads A (*11) 273  220        0  0       Glass beads B (*12)  273 530         0       Aluminum hydroxide (*13)    273 255 151 141           0 0 7 6       Hemihydrate gypsum (*14)        103 133 668               0 5       Alumina cement (*15)           179 235 199 117                  6 1 7 5       Portlant cement (*16)               180 144 144                      0 9 0       Aluminum sulfite (*17)   1.5       Polyethylene oxide (*18)       Water 123 123 123 123 123 123 123 105 105 123 153 135 162 135 180 162     180        0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0       Remark 1        *20 *21 *21 *22 *22 *22 *22       Test results       Bending strength (MPa) (*23) 6.2 6.4 6.3 6.1 6.1 6.2 6.3 5.8 5.9 6.1     5.4 6.2 5.0 6.6 6.4 7.1 6.4       Flexural modulus (MPa) (*23) 105 103 100 960 930 950 970 870 870 900     920 990 870 990 105 110 990        0 0 0            0 0       Deposition rate constant (0.01 mm.sup.2 /sec) (*24) 1.6 1.7 1.7 1.7     1.7 1.6 2.0 1.7 2.0 1.5 1.9 1.7 1.7 1.7 1.8 1.7 1.7       Amount of passed water (1000 mm.sup.3 /3 min.) 100 120 130 45 50 65     110 74 62 100 50 40 55 38       (*25)       Mold releasability strength (0.01 MPa) (*26) 0.3 0.3 0.3 0 0 0 0 0 0 0       0 0 0 0 0 0 0       Emulsion slurry viscosity (mPa.sec) 100   420 380 400 410 540 500 560     380 420 400 410 170 140 160       (*27) 0 950 900 0 0 0 0 0 0 0 0 0 0 0 0 0 0       Remark 2           *29     The unit for specimens is 0.001 kg.     (*: Note)     (1) Bisphenol A epoxy resin (manufactured by Petrochemical Shell Epoxy Co     Ltd.).     (2) Bisphenol AD epoxy resin (manufactured by Mitsui Petrochemical     Industries, Inc.).     (3) Bisphenol F epoxy resin (manufactured by Petrochemical Shell Epoxy Co     Ltd.).     (4) A mixture of mcresyl glycidyl ether and pcresyl glycidyl ether at a     ratio of 1:1 (manufactured by Tokyo Chemical Industries, Inc.).     (5) A product produced by mixing the constituents given below and allowin     them to react in an N2 atmosphere from normal temperature to 230°     C. for 2 hours and at 230 ± 5° C. for 2 hours: 30 wt % of oleic     acid (manufactured by Nippon Oils & Fats Co. Ltd.); 30 wt % of dimer acid     (manufactured by Nippon Oils & Fats Co. Ltd.); and 40 wt % of     tetraethylene pentamine (manufactured by Tokyo Chemical Industries, Inc.)     (6) A polyamide hardener (manufactured by Sanyo Chemical Industries,     Inc.).     (7) A product produced by mixing the constituents given below and allowin     them to react from normal temperature to 80° C. for 20 minutes and     from 80 to 250° C. for 3 minutes: 54 wt % of diethylene triamine     (manufactured by Tokyo Chemical Industries, Inc.); and 46 wt % of ethylen     glycol glycidyl ether (manufactured by Tokyo Chemical Industries, Inc.).     (8) A product produced by mixing the constituents given below and allowin     them to react in an N2 atmosphere from normal temperature to 80° C     for 30 minutes, from 80 to 250° C. for 3 hours, and at 250 ±     5° C. for 1 hour: 1.5 wt % of NAA 35 (monomer fatty acid,     manufactured by Nippon Oils & Fats Co. Ltd.); 56.5 wt % of Varsadime V216     (polymer fatty acid, manufactured by Henkel Japan Co., Ltd.);  # 37 wt %     of tetraethylene pentamine (manufactured by Tokyo Chemical Industries,     Inc.); and 5 wt % of pentaethylenehexamine (manufactured by Tokyo Chemica     Industries, Inc.).     (9) Manufactured by Tokyo Chemical Industries, Inc.)     (10) A powder of siliceous sand having a quartz purity of 98% whose grain     size distribution is shown in Table 4, given below. In Table 4, A     represents a powder of siliceous sand produced in Seto, Japan, which was     ground by a wettype cylindermill, and B ˜ K represent the same     powder of siliceous sand which is classified by centrifugal separation,     sedimentation, or the like, or a  # mixture containing the classified     powder of siliceous sand.     (11) Spherical glass beads (manufactured by Toshiba Barottini Co., Ltd.),     not surfacetreated. The grain size distribution is shown in Table 4.     (12) Spherical glass beads (manufactured by Toshiba Barottini Co., Ltd.),     surfacetreated by a silane coupling agent. The grain size distribution is     shown in Table 4.     (13) Manufactured by Nippon Light Metal Co. Ltd. The average particle     diameter is 4.5 μm.     (14) Manufactured by Nitto Gypsum Co., Ltd. β hemihydrate gypsum.     (15) Manufactured by Asahi Glass Co., Ltd. Main constituents: 56% of     Al.sub.2 O.sub.3, 36% of CaO, 4% of SiO.sub.2, and 1% of Fe.sub.2 O.sub.3     (16) Manufactured by Onoda Cement Co., Ltd. Main constituents: 22% of     SiO.sub.2, 6% of Al.sub.2 O.sub.3, 3% of Fe.sub.2 O.sub.3, 64% of CaO, an     2% of SO.sub.3.     (17) Manufactured by Wako Junyaku Co., Ltd. 18 ˜ 18 hydrate.     (18) Manufactured by Tokyo Chemical Industries, Inc.     (19) Prepared by mixing an epoxy compound and water, adding a filler to     the mixture, intensively stirring the mixing for 20 minutes, then adding     hardener and a hardening accelerator, and intensively stirring the mixtur     for 10 minutes into a uniform emulsion slurry.     (20) Prepared and hardened by mixing gypsum and an epoxy compound,     evacuating the mixture to remove pins for 30 minutes, then cooling the     mixture to  10° C., adding other materials cooled to 4° C.     to the mixture, and stirring the mixture for 10 minutes into an emulsion     slurry. The temperature of the stirred emulsion slurry was 15° C.     The emulsion slurry was hardened at 4° C. for 3 hours,  #     25° C. for 24 hours, and 45° C. for 72 hours.     (21) Prepared and hardened by mixing gypsum and an epoxy compound,     evacuating the mixture to remove pins for 30 minutes, then cooling the     mixture to  18° C., adding water cooled to 4° C. and other     materials cooled to  18° C. to the mixture, and stirring the     mixture for 10 minutes into an emulsion slurry while cooling the     container. The temperature of the stirred emulsion slurry was 5° C     The emulsion slurry was  # hardened at 4° C. for 3 hours,     25° C. for 24 hours, and 45° C. for 72 hours.     (22) Prepared and hardened by mixing alumina cement and water, evacuating     the mixture to remove pins for 1 hour, adding other materials to the     mixture, and stirring the mixture for 10 minutes into an emulsion slurry.     The emulsion slurry was hardened at 20° C. for 24 hours and     45° C. for 24 hours.     (23) The bending strength and the flexural modulus were measured as     follows: Test piece dimensions: 15 mm × 15 mm × 120 mm;     Threepoint bending; Span: 100 mm; Head speed: 2.5 mm/min.; The test piece     was fully saturated by evacuating the test piece for 30 minutes, immersin     the test piece in water, and then further evacuating the test piece for 3     minutes.     (24) The deposition rate constant was measured as follows: I) A test piec     having a size of 100 mm φ × 30 mm t was adjusted to a water     saturation percentage of 50%; II) A glass tube of 60 φ was vertically     placed on the test piece, and a slurry of vitreous china for sanitary     earthenware was poured into the glass tube to a depth of 50 mm. Test     results for those using slurries other than the  # slurry for sanitary     earthenware are given in Remark 2; III) After the assembly was left to     stand until a layer was deposited to a thickness of 8 mm as observed from     outside of the glass tube, the slurry which was not deposited was     discharged; IV) The remaining slurry attached to the surface of the     deposited layer was cleaned away; V) The thickness L (mm) of the central     portion of the deposited layer was measured; and VI) The deposition rate     # constant was calculated according to k = L.sup.2 /t.     (25) The amount of passed water was measured as follows: I) A test piece     having a size of 100 mm φ × 30 mm t was fully saturated after     its side was completely sealed; and II) A water pressure of 0.3 MPa was     applied to one end of the test piece, and the amount of water discharged     from the other end of the test piece was measured in 3 minutes after the     water pressure started to be applied.     (26) The mold releasability strength was measured as follows: I) A test     piece having a size of 100 mm φ × 30 mm t was adjusted to a     water saturation percentage of 50%; II) A glass tube of 60 φ was     vertically placed on the test piece, and a slurry of vitreous china for     sanitary earthenware was poured into the glass tube to a depth of 50 mm.     Test results for those using slurries other than the slurry for sanitary     earthenware are given in Remark 2;  # III) After the assembly was left to     stand until a layer was deposited to a thickness of 8 mm as observed from     outside of the glass tube, the slurry which was not deposited was     discharged; IV) The glass tube standing on the test piece was inverted in     erected condition to prevent the molded body from being dried, and left t     stand for 30 minutes; V) After the test piece was fixed, the glass tube     was pulled by using an autograph, measuring forces  # required to remove     the molded body. The glass tube has notches defined therein to enable the     molded body to be released from the test piece reliably without allowing     the molded body to remain attached to the test piece; VI) A value     calculated by dividing the measured forces by the area of the deposited     layer was used as the mold releasability strength. Those mold     releasability strength values which were very small, with the readings on     the autograph  # remaining substantially the same as the total weight of     the glass tube and the molded body, were assumed to be nil. Test results     for those using slurries other than the slurry for sanitary earthenware     are given in Remark 2.     (27) The viscosity of the stirred emulsion slurry was measured by a     Brookfield viscometer.     (28) An evaluation test was conducted using the following slurries: The     apparent thickness of the deposited layer was 4 mm, and the period of tim     for which the molded body was left to stand after discharging the slurry     was 15 minutes. Slurry for tableware porcelain: k = 0.85 (×     10.sup.-2 mm.sup.2 /sec), mold releasability strength: 1.2 (×     10.sup.-2 MPa); Highly pure alumina slurry:  # k = 0.42 (× 10.sup.-     mm.sup.2 /sec), mold releasability strength: 0.1 (× 10.sup.-2 MPa);     and Iron slurry for powder metallurgy: k = 3.9 (× 10.sup.-2 mm.sup.     /sec), mold releasability strength: 0.1 (× 10.sup.-2 MPa).     (29) An evaluation test was conducted using the following slurries: The     apparent thickness of the deposited layer was 4 mm, and the period of tim     for which the molded body was left to stand after discharging the slurry     was 15 minutes. Slurry for tableware porcelain: k = 0.81 (×     10.sup.-2 mm.sup.2 /sec), mold releasability strength: 0 (×     10.sup.-2 MPa); Highly pure alumina slurry: k = 0.53 (× 10.sup.-2     mm.sup.2 /sec),  # mold releasability strength: 0 (× 10.sup.-2 MPa)     and Iron slurry for powder metallurgy: k = 4.4 (× 10.sup.-2 mm.sup.     /sec), mold releasability strength: 0 (× 10.sup.-2 MPa).

                                      TABLE 4                                     __________________________________________________________________________             Grain size distribution        Absolute size                                  ˜ 0.2                                                                      ˜ 0.5                                                                      ˜ 1.0                                                                      ˜ 2.0                                                                      ˜ 5.0                                                                      ˜ 10                                                                       ˜ 15                                                                       ˜ 20                                                                       Absolute size                                                                        constant sieve                          Filler μm μm μm μm μm μm μm μm constant (μm)                                             volume (%)                            __________________________________________________________________________    Powder of siliceous                                                                    17.8                                                                             29.9                                                                             37.4                                                                             45 57.5                                                                             67 72.8                                                                             77.5                                                                             7.1    43                                      sand A                                                                        Powder of siliceous 9.8 17.8 27.5 42.8 67 84.5 92 96.9 4.2 29                 sand B                                                                        Powder of siliceous 4.1 10.9 19.5 42 74.2 95.7 98.8 99.7 3.7 20                                                      sand C                                 Powder of siliceous 1.4 4.7 13.3 35.6 86.1 99.7 100 100 3.3 11                sand D                                                                        Powder of siliceous 0 1.6 7.1 30.7 96.5 99.8 100 100 3  4                     sand E                                                                        Powder of siliceous 2.8 10.4 21.8 45.5 78.5 80.1 96.8 99.3 3.2 18                                                    sand F                                 Powder of siliceous 29.8 58 76.1 90.9 98.9 99.9 100 100 0.6 25                sand G                                                                        Powder of siliceous 5.4 15.5 22.5 60 94 99.5 100 100 2.1 17                   sand H                                                                        Powder of siliceous 0.7 1.4 3.2 9.1 55.1 98.1 99.8 100 5.5  5                 sand I                                                                        Powder of siliceous 0.4 0.7 0.9 1.2 10 89.4 98.5 99.8 8.2  1                  sand J                                                                        Powder of siliceous 0.2 0.4 0.6 0.8 1.7 10.2 36.1 63.2 20  2                  sand K                                                                        Glass beads A 0 0 1.4 20.7 99.9 100 100 100 2.7  0                            Glass beads B 0 0 0 0 12.8 90.3 100 100 8  0                                __________________________________________________________________________     Indicated numerical values represent integrated sieved volume %.         

Pieces of sanitary earthenware were slip cast under casting conditionsshown in Table 5, using a slip casting mold having the structure shownin FIG. 6 whose water absorption layer comprised the open porous bodyproduced in Specimen 5. Results of evaluation of the produced pieces ofsanitary earthenware are shown in Table 5. In any of Examples shown inTable 5, the slurry was not directly pressurized.

In FIGS. 1, 2, 4, 5 and 6, the reference numeral 8 represents a cassettecase, 9 an open porous body layer, 10 a hollow path (air groove), 11pipes interconnecting the air groove and sources outside of the mold, 12backing layers, 13 mating surfaces, 14 resin layers as a sealant, 15 aslip casting space, 16 a slurry delivery pipe, 17 a slurry drainingpipe, 18 a three-way cock, 19 a compressed air inlet pipe, 20 a checkvalve, 21 a molding surface, and 22 a coarse porous layer.

                                      TABLE 5                                     __________________________________________________________________________                         Ex. 1                                                                            Ex. 2                                                                            Ex. 3                                                                            Ex. 4                                                                            Ex. 5                                                                            Ex. 6                                                                            Ex. 7                                                                            Ex. 8                                                                             Ex. 9                                                                             Ex. 10                                                                            Ex. 11                                                                            Remarks             __________________________________________________________________________    Mold Water saturation                                                                      Water passing                                                                         -- -- -- 4  4  3  4  --  --  --  --                          time (min.)                                                                 water  Air pressure -- -- -- 0.3 0.35 0.4 0.4 -- -- -- --                       (MPa)                                                                       satura- Water drainage Water drainage 4 3 1 1 1 -- -- 1 0.7 1 0.7                                                                      tion  time                                                                   (min.)                  Air pressure 0.3 0.35 0.35 0.25 0.25 -- -- 0.2 0.2 0.15 0.15                  (MPa)                                                                     condi-                                                                             Mold water saturation percentage (%)                                                          18.6                                                                             27.0                                                                             38.5                                                                             52.3                                                                             60.7                                                                             72.1                                                                             81.9                                                                             55.8                                                                              62.1                                                                              70.7                                                                              78.4                      tions                                                                         Molding Evacuating time (min.) 83 80 70 45 50 85 93 76 39 25 40                                                                        condi-                                                                       Evacuating                                                                    pressure (MPa)                                                                0.07 0.07 0.05                                                                0.05 0.05 0.07                                                                0.07 0.07 0.07                                                                0.07 0.07                                                                     #1 #3                 tions            0.02#2                                                        Pouring time (min.) 5 5 5 5 5* 5* 5* 5* 5* 4* 3.5                             Deposition time (min.) 52* 50* 45* 45* 45* 50* 55* 50* 48 (70) 42 (50)                                                               40*                    Slurry head height (m) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.45 0.7 1.2 2                                                                      Slurry                                                                      draining time                                                                 (min.) 5* 5* 5*                                                               5 5 5* 5* 5* 5                                                                5 5 #4                 Slurry draining air pressure (MPa) 0.02 0.02 0.02 0.02 0.02 0.02 0.02                                                                0.02 0.02 0.02                                                                0.02 #5                                                                         Compaction                                                                  time (min.) 26*                                                               25* 20* 20 20                                                                 25* 28* 23 (70)                                                               20 19 17 #6                                                                     Compaction                                                                  air pressure                                                                  (MPa) 0.01 0.01                                                               0.01 0.01 0.01                                                                0.01 0.01 0.08                                                                4 0.02 0.02                                                                     Mold release                                                                air pressure                                                                  (MPa) 0.30 0.30                                                               0.27 0.25 0.25                                                                0.23 0.23 0.25                                                                0.25 0.25 25.00     Results                                                                            Molded product                                                                        Single layer                                                                          8.7                                                                              8.8                                                                              9.0                                                                              9.1                                                                              9.2                                                                              8.8                                                                              8.5                                                                              9.0 9.1 8.9 8.9 #7                      thickness (mm)                                                                Water content 25.6 24.9 24.5 24.1 24.2 24.7 26.2 24.8 24.5 24.7 24.2                                                                   percentage                                                                 (%)                      Mold releasability                                                                            X  ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     #8                     Molded product shape retention X ◯ ◯ .largecirc                                                              le. .largecircle                                                              . ◯                                                               X ◯                                                               ◯                                                                 ◯                                                                 ◯                                                                 #9                     Molded product surface peel-off X ◯ ◯ .circle-w                                                              /dot. .circle-w/                                                              dot. .largecircl                                                              e. ◯                                                               ⊙                                                               ⊙                                                                ⊙                                                                ⊙                                                                #10                 __________________________________________________________________________     #1: Former 30 minutes.                                                        #2: Latter 30 minutes.                                                        #3: Indicates a gage pressure upon evacuation.                                #4: * represents combination with evacuation.                                 #5: () represents combination with evacuation during a former half of         deposition and compaction time.                                               #6: The numerical values in () represent % of the evacuating time during      the former half of deposition and compaction time.                            #7: Target value: 9.0 ± 0.2                                                #8: ⊙ Very good.                                                 #9: ◯ Good.                                                       #10: X Poor.                                                             

A successive slip casting process was carried out under the castingconditions of Example 9 in Table 5. As a result, 5000 molded productswere produced by the slip casting mold in Example 9. After the slipcasing mold was used 5000 times, no reduction was seen in the depositionrate and the mold releasability.

Although there have been described what are at present considered to bethe preferred embodiments of the invention, it will be understood thatthe invention may be embodied in other specific forms without departingfrom the essential characteristics thereof. The present embodiments aretherefore to be considered in all respects as illustrative, and notrestrictive. The scope of the invention is indicated by the appendedclaims rather than by the foregoing description.

What is claimed is:
 1. A method of slip casting a powdery material witha slip casting mold having a self water absorption capability and awater absorption layer which is substantially water resistant,comprising the steps of:I) controlling a water saturation percentage ofthe water absorption layer; II) pouring a slurry into the slip castingmold; III) depositing the slurry on the water absorption layer under aslip casting pressure which comprises a pressure selected from at leastone of a) a slurry head pressure, b) a suction vacuum applied to thewater absorption layer, and c) a pressure of at most 0.3 MPa applieddirectly to the slurry; and IV) releasing a deposited molded body fromthe slip casting mold.
 2. A method according to claim 1, wherein saidstep III) comprises the step of depositing the slurry on the waterabsorption layer under a) the slurry head pressure.
 3. A methodaccording to claim 1, wherein said step III) comprises the step ofdepositing the slurry on the water absorption layer under a) the slurryhead pressure and b) the suction vacuum applied to the water absorptionlayer.
 4. A method according to claim 1, wherein said water absorptionlayer is evacuated in the step II).
 5. A method according to claim 2,wherein b) the suction vacuum applied to the water absorption layer insaid step III) is applied for a period of time selected in a period froma start of said step III) to 80% of a time required to complete saidstep III).
 6. A method according to claim 1, wherein b) the suctionvacuum applied to the water absorption layer in said step III) isprogressively reduced as the step III) progresses.
 7. A method accordingto claim 1, further comprising, prior to the step IV), the steps of:1)discharging an excessive slurry; and 2) lowering a water contentpercentage of a slurry draining surface of the deposited molded body toincrease a hardness of the deposited molded body.
 8. A method accordingto claim 7, wherein the water content percentage of the slurry drainingsurface of the deposited molded body is lowered to increase the hardnessof the deposited molded body by introducing air under pressure into aslurry draining space in the slip casting mold.
 9. A method according toclaim 7, wherein the water content percentage of the slurry drainingsurface of the deposited molded body is lowered to increase the hardnessof the deposited molded body by introducing air under pressure into aslurry draining space in the slip casting mold and applying a suctionvacuum to the water absorption layer.
 10. A method according to claim 9,wherein the suction vacuum applied to the water absorption layer isapplied for a period of time selected in a period extending from an endof the step of discharging the excessive slurry to 80% of a timerequired by the step of lowering the water content percentage of theslurry draining surface.
 11. A method according to claim 9, wherein thesuction vacuum applied to the water absorption layer is progressivelyreduced as the step of lowering the water content percentage of theslurry draining surface progresses.
 12. A method according to claim 1,wherein a) the slurry head pressure is applied by a slurry head heightof at least 0.4 m.
 13. A method according to claim 1, wherein said stepI) involves introducing air under pressure into the slip casting mold todischarge water from the water absorption layer.
 14. A method accordingto claim 1, wherein said step I) involves introducing water underpressure into the slip casting mold to discharge air from the waterabsorption layer.
 15. A method according to claim 1, wherein said stepI) involves introducing water under pressure into the slip casting moldto discharge air from the water absorption layer, and thereafterintroducing air under pressure into the slip casting mold to dischargewater from the water absorption layer.
 16. A method according to claim1, wherein said step IV) involves introducing at least one of air andwater under pressure into the slip casting mold.
 17. A method accordingto claim 13, wherein the air under pressure is introduced into the slipcasting mold through air grooves defined inside or in a reverse side ofthe water absorption layer.
 18. A method according to claim 13, whereinthe air under pressure is introduced into the slip casting mold througha coarse porous layer disposed on a reverse side of the water absorptionlayer and having a pipe extending out of the slip casting mold forpassing water and air therethrough.
 19. A method according to claim 17,wherein said air grooves are connected into a plurality of main airgrooves which are connected to a pipe extending out of the mold forpassing water and air therethrough.
 20. A method according to claim 18,wherein said coarse porous layer has a plurality of pipes extending outof the slip casting mold for passing water and air therethrough.
 21. Amethod according to claim 1, wherein said step I) involves controllingthe water saturation percentage of the water absorption layer at a rangefrom 30 to 80%.
 22. A method according to claim 1, wherein a pluralityof said steps are grouped in a block, and the steps in each block arecarried out in each of a plurality of stations, and wherein the slipcasting mold is movable between said stations.
 23. A method according toclaim 1, wherein said molded body is one of ceramic whiteware sanitaryearthenware, fine ceramics, and a powder metallurgy product.
 24. Amethod according to claim 1, wherein said step I involves controllingthe water saturation percentage of the water absorption layer within apredetermined range.
 25. A method according to claim 24, wherein saidpredetermined range is less than 100% saturation.